(i) Field of the Invention
The present invention relates to an optical disc recording apparatus.
(ii) Description of the Related Art
In the field of optical discs such as a CD-R (Compact Disc Recordable) and a CD-RW (Compact Disc ReWritable), a technique becomes widespread which utilizes a laser beam or the like to record information at a high speed with high density, for example, a CAV (Constant Angular Velocity) recording technique which sets a number of revolutions of an optical disc constant and changes a basic clock frequency of a recording signal in accordance with a position of an optical head.
In an optical disc apparatus adopting such a CAV recording system, a linear velocity (relative velocity of an optical disc to a laser spot) varies during recording of the signal. In order to perform accurate writing processing on the optical disc without varying the laser power used for writing information, a write pulse used for writing information on the optical disc must be optimized in accordance with a linear velocity. As a method for controlling such a write pulse, there are proposed a method which changes a duty ratio of the pulse in accordance with a linear velocity (which will be referred to as a pulse width fixed type hereinafter), and another method which changes a pulse width in accordance with a linear velocity (which will be referred to as a duty ratio fixed type hereinafter) and others.
FIG. 16(a) is a view for explaining a write pulse control method which is of the pulse width fixed type, and FIG. 16(b) is a view for explaining a write pulse control method which is of a duty ratio fixed type.
As shown in FIG. 16(a), in the write pulse control method which is of the pulse width fixed type, control is effected in such a manner that a pulse width TX at recording on the inner peripheral side of an optical disc where a linear velocity is small becomes equal to a pulse width TY at recording on the outer peripheral side of the optical disc where a linear velocity is large. Specifically, when a pulse cycle T1 on the inner peripheral side is set to 50 μsec; a pulse cycle T2 on the outer peripheral side, 20 μsec; and a pulse width TX on the inner peripheral side, 0.2*T1, the pulse width TY on the outer peripheral side is set to 0.5*T2 based on the following expressions (a) to (d). It is to be noted that each of the pulse cycles T1 and T2 represents a time required for forming one pit on the optical disc.                     TX        =                              0.2            *            T1                    =                      10            ⁢                                                  ⁢            µsec                                              (        a        )                                TY        =                  TX          =                      10            ⁢                                                  ⁢            µsec                                              (        b        )                                          T2          ⁢                      :                    ⁢          TY                =                  20          ⁢                      :                    ⁢          10                                    (        c        )                                TY        =                                            10              /              20                        *            T2                    =                      0.5            *            T2                                              (        d        )            
On the other hand, in the write pulse control method which is of the duty ratio fixed type, as shown in FIG. 16(b), control is effected in such a manner that a duty ratio DX on the inner peripheral side becomes equal to a duty ratio DY on the outer peripheral side. Specifically, when the pulse width TX on the inner peripheral side is set to 0.5*T1 (assuming that a pulse cycle on the inner peripheral side is T1 and a pulse cycle on the outer peripheral side is T2), the pulse width TY on the outer peripheral side is set to 0.5*T2 based on the following expressions (e) to (g).                     DX        =                              0.5            *                          T1              /              T1                                =          0.5                                    (        e        )                                DY        =                  DX          =          0.5                                    (        f        )                                TY        =                  0.5          *          T2                                    (        g        )            
The above-described write pulse control methods of the pulse width fixed type and the duty ratio fixed type are not necessarily always optimum. That is, determination of an optimum value of a compensation amount of the write pulse (which will be referred to as a strategy hereinafter) differs depending on a linear velocity as well as a structure or a type of the optical disc which is an information recording target. For example, in case of recording information on a specific optical disc, it may be possible to set an optimum strategy. However, in case of recording information on an optical disc which is a different type from the former optical disc, an optimum strategy may not be set, and there is a problem of, e.g., occurrence of a recording error or the like.